London, England March 31, 1939

On this date in 1939, two weeks after German troops entered Prague and all of Czecho­slo­va­kia fell under the German boot, the British govern­ment, followed a few days later by the French, pledged to guar­an­tee the inde­pen­dence (though inter­estingly not the terri­torial integ­rity) of Poland. “If any action clearly threatened Polish inde­pen­dence,” the British secu­rity guaran­tee read, “and if the Poles felt it vital to resist such action by force, Britain would come to their aid.” A week later, when Polish Foreign Minis­ter Józef Beck visited London, Britain and Poland agreed to begin talks with the inten­tion of formal­izing a mili­tary alli­ance. The idea of an alli­ance, which had broad public support, was a sym­bolic line in the sand drawn by Britain and France, both nations viewing Poland as the next target of Adolf Hitler’s seemingly bound­less aggres­sion. Stepping over that line, which was meant to “de-risk” the out­break of war, would have con­se­quences. (It goes almost with­out saying that the Anglo-French security guar­an­tee of March and April 1939 was unenforce­able with­out assistance from Poland’s eastern neighbor, the Soviet Union.)

That the Western democracies would guarantee Poland’s inde­pen­dence so enraged Hitler that he told com­man­ders of his Wehr­macht (German armed forces) to begin stra­tegic plan­ning for Fall Weiss (Oper­a­tion White), the destruc­tion of Poland, with a pro­vi­sional start date of Septem­ber 1, 1939. A defeated Poland would elim­i­nate the “Free City of Danzig” (German, Freie Stadt Danzig), con­sisting of the Bal­tic sea­port of Dan­zig (today’s Gdańsk) and sur­rounding areas, which were roughly 95 per­cent ethnic German. This geo­graphi­cal oddity of the 1919 Ver­sailles Peace Treaty was admin­is­tered by a League of Nations high com­mis­sioner (at the time, a Swiss), and most Germans found Danzig’s exis­tence a vexa­tion because it and the so-called Polish Corri­dor east of Danzig split East Prus­sia from West Prus­sia and the rest of Nazi Ger­many (see map). Ger­man units were to in­vade Poland from three direc­tions: the main attack from Germany across the west­ern Polish border, a second route from the East Prus­sian enclave, and a third attack by German and allied Slo­vak units from the Czech puppet state (since March 14, 1939) of Slo­va­kia. All three assaults were to con­verge on Warsaw, the Polish capital.

Fall Weiss was the first European military oper­a­tion of World War II. It would be six years of bru­tal occu­pa­tion and the death of four mil­lion Polish civil­ians, three-quarters of them Jews who died in con­cen­tra­tion camps or gas cham­bers, before the last units of the Wehr­macht were swept from Polish soil. As for Danzig itself, many of its resi­dents perished or fled west­ward ahead of the Soviet on­slaught and the city’s destruc­tion and con­quest by the Red Army in March 1945. After the war most of the remaining ethnic Germans were forcibly expelled. The city was sub­se­quently placed under Polish admin­is­tra­tion by the Allied Pots­dam Agree­ment (August 1, 1945), and Poles from Central and Soviet-an­nexed Eastern Poland were brought in to replace the German population.

German Conquest of Poland, September 1 to October 6, 1939

Map of Danzig (Gdańsk), 1939

Above: Map of Danzig (“Free City of Danzig,” present-day Gdańsk) and Poland’s corri­dor to the Baltic Sea (“Polish Corri­dor”) squeezed between German West and East Prus­sia on the eve of war, 1939. The Memel Terri­tory (today’s Kalinin­grad Oblast) was retrans­ferred by an intim­i­dated Lithu­ania to Nazi Ger­many on March 23, 1939. This event proved to be the last of a series of blood­less annex­a­tions of terri­tories sep­a­rated from Germany by the 1919 Treaty of Versailles.

Britain guarantees Poland independence: German troops remove Polish insignia near Sopot, Poland, 1939Germany invades Poland: German and Slovak soldiers in Southeastern Poland, 1939

Left: German troops remove Polish insignia at the Polish-Danzig border near Sopot (German, Zoppot), September 1, 1939.

Right: German and Slovak soldiers pose with civilians in Komańcza, Southeastern Poland, September 1939.

Germany invades Poland: German cavalry and motorized units, Poland 1939Germany invades Poland: Royal Castle in Warsaw burning, 1939

Left: German cavalry and motorized units enter Poland from East Prussia, 1939.

Right: The Polish Royal Castle in Warsaw on fire after being shelled by Germans, Septem­ber 17, 1939. On Septem­ber 26 German troops captured three key forts defending Warsaw and entered the capital the next day.

Silent German Propaganda Film “Liberation” of Danzig and Wehrmacht’s Assault on Poland, September 1939